Single or multi-layer printed circuit board with recessed or extended breakaway tabs and method of manufacture thereof

ABSTRACT

A circuit board layer  2  in accordance with the present invention includes a conductive sheet  4  sandwiched between an insulating top layer  10  and an insulating bottom layer  14 . The top and bottom layers  10  and  14  and the conductive sheet  4  define the circuit board layer  2  having an edge that includes an edge  20  of the conductive sheet  4 . An insulating edge layer  18  covers substantially all of the edge  20  of the conductive sheet  4.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part from U.S. patent applicationSer. No. 10/184,387, filed Jun. 27, 2002, entitled “Process for CreatingVias for Circuit Assemblies”.

BACKGROUND OF THE INVENTION

Presently, printed circuit boards are fabricated as part of a largerpanel. Each printed circuit board can be configured in any shape,although most printed circuit boards in common use are made inrectangular shapes of standard sizes. When fabrication of a printedcircuit board is complete, it is cut and separated from the largerpanel, mostly by way of a machine cutting or routing process in which achannel is cut around the printed circuit board. In certain designs, thechannel around the printed circuit board does not completely encirclethe perimeter of the printed circuit board. Rather, tabs are left atseveral places around the perimeter of the printed circuit board toattach it to the larger panel until the board is singulated from thelarger panel by breaking the tabs. Typically, metal planes in theprinted circuit board do not extend to its edge where they would be cutby the routing process. In this way, no conductive metal is left exposedon the edges of the printed circuit board.

The existing methods of cutting printed circuit boards from largerpanels are unsatisfactory for high density boards because the limiteddimensional stability of the printed circuit boards does not allowregistration of one high density pattern to the next on the largerpanel. Cut lines made around the periphery of the printed circuit boardfurther weaken the panel material, exasperating misregistration of onepattern to the next.

Electronic systems assembled onto conventional printed circuit boardsrely upon thermal conduction from integrated circuits dissipating heatto the printed circuit board to remove some of the heat from theintegrated circuits. For intermediate ranges of heat, up to about 2watts per chip, conduction to the printed circuit board is sufficient tocool the integrated circuits without the need for bulky and expensiveheat sinks. In high performance systems, however, as the density of thesystem and the percentage of the substrate covered by the integratedcircuits increases, the thermal path to the printed circuit board isless efficient. At a point when the density of the system increasessufficiently, the printed circuit board is not effective as a heat sinkfor the integrated circuits. However, the need for effective thermalconduction from the integrated circuits to the substrate and therefromto the ambient becomes more important as system density increases.Because of the evolution toward higher system density and largerintegrated circuit coverage, means are needed for cooling the substratein order to maintain the integrated circuits on the substrate at a safeoperating temperature.

In addition to thermal conduction, high performance systems increasinglyrequire low impedance power and ground voltage supplies to run theintegrated circuits at high clock speeds. Typically, the AC impedancesof power and ground supplies are lowered by the use of low impedancebypass capacitors connected to the power and ground planes. Onconventional printed circuit boards, capacitors are connected to powerand ground planes through vias which extend through some thickness ofthe board, increasing the impedance of this contact and degradingperformance of the system. As switching speeds increase, the problem ofmaking low impedance connections between bypass capacitors and the powerand ground planes becomes more important.

It is, therefore, an object of the present invention to overcome theabove problems and others by providing a printed circuit board havingone or more printed circuit board layers having a conductive plane whichextends to the edge of the printed circuit board but which issubstantially, but not completely, covered by an insulating material.The edge of the conductive layer not covered by the insulating materialcan be on the edge of a tab which is utilized to couple the board to adisposable part of a larger panel that the board is formed from duringfabrication. The exposed edge of the conductive layer becomes exposedupon breaking the tab and singulating the printed circuit board from thedisposable part of the larger panel. In one embodiment, the tabterminates in a recess in the perimeter of the printed circuit board. Inanother embodiment, the tab extends outward from the perimeter of theprinted circuit board.

The conductive plane can be formed from metal, such as a copper foil,that can serve the dual purpose of conducting heat away from electricalcomponents disposed on one or both surfaces of the printed circuit boardor printed circuit board layer and for providing power or ground to theelectrical components. The tab which extends outward from the edge ofthe second embodiment of the printed circuit board can be coupled to amechanical fixture and/or an electrical fixture to provide a path forthe flow of heat from the printed circuit board to externally coupledmechanical fixtures and/or to provide electrical power to theelectrically conducting layer of the printed circuit board. Still otherobjects will become apparent to those of ordinary skill in the art uponreading and understanding the following detailed description.

SUMMARY OF THE INVENTION

The present invention is a circuit board that includes a conductivesheet sandwiched between an insulating top layer and an insulatingbottom layer. The top and bottom layers and the conductive sheet definea circuit board layer having an edge that includes an edge of theconductive sheet. An insulating edge layer covers substantially all ofthe edges of the conductive sheet.

The conductive sheet can include at least one via therethrough. Theinsulating layers can be formed from a common dielectric materialdeposited on the conductive sheet in a manner known in the art, such asconformal coating. At least one of the top and bottom layers can have acircuit pattern formed thereon.

The insulating edge layer can include at least one opening where a partof the edge of the conductive sheet is exposed in response to separatingthe circuit board layer from a panel. In one embodiment, the exposedpart of the edge can be within a perimeter of the circuit board layer.Moreover, the exposed part of the edge can be on a tab attached to thecircuit board layer where the tab extends into a recess in the circuitboard layer.

The top and bottom insulating layers and the conductive sheet define apanel that includes the circuit board layer coupled to a disposable partof the panel by the tab. The insulating edge layer covers the edges ofthe tab and the circuit board layer prior to singulation of the circuitboard layer from the disposable part of the panel. The tab is responsiveto a breaking force applied thereto for breaking whereupon the circuitboard layer separates from the disposable part of the panel with atleast part of the tab remaining attached to the circuit board layer.

In another embodiment, the conductive sheet includes a tab that extendsoutward from between the top layer and the bottom layer. At least partof the edge of the tab is exposed when the circuit board layer isseparated from the disposable part of the panel. The at least part ofthe edge is outside a perimeter of the circuit board layer. The tab inthis embodiment has a top surface and a bottom surface. At least part ofone of the top surface and the bottom surface of the tab can be exposed,i.e., not covered by insulating material.

A plurality of circuit board layers can be laminated together to form amulti-layer circuit board. The tab of one circuit board layer of themulti-layer circuit board can be offset from the tab of another circuitboard layer of the multi-layer circuit board. An electronic componentcan be connected between the tab of one circuit board layer and the tabof the other circuit board layer. The conductive sheet of one circuitboard layer can define the ground plane of the multi-layer circuit boardand the conductive sheet of another circuit board layer can define apower plane of the multi-layer circuit board.

The invention is also a method of forming a circuit board that includesproviding a first conductive sheet and selectively removing one or moreportions of the first conductive sheet to form a first panel having afirst circuit board that is coupled to a disposable part of the firstpanel by at least one tab that extends from an edge of the first circuitboard to an edge of the disposable part of the first panel. Aninsulating coating is applied to the first circuit board so at leasteach edge of the first circuit board is covered thereby. The firstcircuit board is separated from the disposable part in a mannerwhereupon at least part of the tab remains attached to the first circuitboard and this part of the tab includes an exposed edge of theconductive sheet of the first circuit board.

The insulating coating can be applied to the first circuit board in amanner whereupon at least each edge of the at least one tab is coveredthereby. The at least part of the tab can terminate one of inside andoutside a perimeter of the first circuit board.

The method can also include providing a second conductive sheet andselectively removing one or more portions of the second conductive sheetto form a second panel having a second circuit board that is coupled toa disposable part of the second panel by at least one tab that extendsfrom an edge of the second circuit board to an edge of the disposablepart of the second panel. An insulating coating is applied to the secondcircuit board so that at least each edge of the second circuit board iscovered thereby. The first and second circuit boards are then laminatedtogether and the second circuit board is separated from the disposablepart of the second panel in a manner whereupon at least part of the tabremains attached to the second circuit board and the at least part ofthe tab includes an exposed edge of the conductive sheet of the secondcircuit board.

The at least part of each tab can terminate inside or outside aperimeter of the corresponding circuit board. When the first and secondcircuit boards are laminated together, the at least one tab of the firstcircuit board is offset from the at least one tab of the second circuitboard. An electrical component can be electrically connected between theat least one tab of the first circuit board and the at least one tab ofthe second circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway perspective view of a printed circuit board layerhaving a perforate conductive plane surrounded by an insulating materialin accordance with the present invention;

FIG. 2 is a cutaway perspective view of a portion of a printed circuitboard layer of the type shown in FIG. 1 including a circuit patternformed on the outward facing surfaces thereof;

FIGS. 3 and 4 are plan views of panels having different circuit boardlayers formed therefrom in accordance with one embodiment of the presentinvention;

FIG. 5 is a plan view of the panels shown in FIGS. 3 and 4 laminatedtogether with the circuit board layers thereof in registry;

FIG. 6 is an isolated plan view of a tab which the panels in FIGS. 3 and4 utilize to connect their circuit board layers to disposable parts ofthe panels;

FIG. 7 is an isolated plan view of the tab shown in FIG. 6 afterbreaking in response to the application of a breaking force appliedthereto;

FIG. 8 is a view taken along lines VIII—VIII in FIG. 7;

FIGS. 9 and 10 are plan views of panels including printed circuit boardlayers in accordance with another embodiment of the present invention;

FIG. 11 is a plan view of the panels shown in FIGS. 9 and 10 laminatedtogether with the circuit board layers thereof in registry;

FIG. 12 is a plan view of the laminated printed circuit board layersshown in FIG. 11 singulated from the disposable parts of theirrespective panels;

FIG. 13 is a section taken along XIII—XIII in FIG. 12; and

FIG. 14 is a plan view of the singulated laminated circuit board layersshown in FIG. 12 with certain tabs thereof coupled to a mounting fixtureand with certain tabs thereof coupled to an electrical fixture.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a printed circuit board layer 2 includes anelectrically conductive sheet or foil 4. Sheet 4 can be formed from acopper foil, an iron-nickel alloy, or combinations thereof. Sheet 4 canbe a perforate sheet as shown in FIG. 1 or can be a solid sheet. It isdesirable for sheet 4 to have a coefficient of thermal expansioncomparable to that of silicon materials from which integrated circuitsare typically prepared in order to prevent failure of adhesion jointsutilized to adhere the integrated circuit or a packaged integratedcircuit (not shown) to printed circuit board layer 2. Describing sheet 4as perforate means that sheet 4 is a mesh sheet having a plurality ofthrough-holes or vias 6 spaced at regular intervals.

An electrically insulative coating 8 is formed around sheet 4. Thiscoating 8 can be formed around sheet 4 in any manner known in the art,such as conformal coating. More specifically, coating 8 forms aninsulating top layer 10 which covers a top surface 12 of sheet 4, aninsulating bottom layer 14 which covers a bottom surface 16 of sheet 4and an insulating edge layer 18 which covers an edge 20 of sheet 4. Whensheet 4 is coated with coating 8, an interior surface of eachthrough-hole or via 6 is also coated with coating 8. Thus, no portion ofsheet 4 is left uncovered by coating 8.

With reference to FIG. 2, and with continuing reference to FIG. 1,printed circuit board layer 2 formed in the above-described manner canhave a conductive pattern formed on the outward facing surface of toplayer 10 and/or the outward facing surface of bottom layer 14 byconventional processes. Specifically, utilizing one or morephotolithographic techniques and one or more metallization techniques,the conductive pattern can be formed on the outward facing surface oftop layer 10 and/or the outward facing surface of bottom layer 14. Thisconductive pattern can include un-plated through-holes or vias 6-1,plated, blind through-holes or vias 6-2, and/or plated through-holes orvias 6-3. Additional details regarding formation of printed circuitboard layer 2 and for forming a conductive pattern, including one ormore of the various types of through-holes or vias 6, on top layer 10and/or bottom layer 14 can be found in U.S. patent application Ser. No.10/184,387, filed Jun. 27, 2002, entitled “Process For Creating Vias ForCircuit Assemblies” which is assigned to the same Assignee as thepresent application and which is incorporated herein by reference.

The preparation of one or more printed circuit board layers 2 in a panelform and the assembly of plural printed circuit board layers to form amulti-layer printed circuit board assembly will now be described.

With reference to FIG. 3, in accordance with a first embodiment of theinvention, one or more first printed circuit board (PCB) layers 30 arefabricated as part of a panel 32. Each first PCB layer 30 is surroundedby a disposable part 34 of panel 32. In accordance with the presentinvention, each first PCB layer 30 is coupled to disposable part 34 ofpanel 32 by one or more tabs 36.

The general steps to prepare panel 32 to the form shown in FIG. 3 willnow be described. Initially, a first conductive sheet, like conductivesheet 4, of the size of panel 32 is provided. This sheet can either be asolid sheet or a perforate sheet depending on the application. Next, cutlines or slots 38 are formed in the conductive sheet by pattern etchingor a machine cutting or routing process to define the perimeter of eachfirst PCB layer 30 of panel 32. These slots 38 are interrupted by tabs36 which hold each first PCB layer 30 to disposable part 34 duringprocessing.

Next, an electrically insulative coating, like coating 8, is depositedon the conductive sheet forming panel 32 in a manner whereupon the topsurface, the bottom surface, and the edges of the electricallyconductive sheet associated with each first PCB layer 30 that wereexposed during the formation of slots 38 are covered thereby. If theconductive sheet is perforate, the electrically insulative coating alsocovers the interior surface of each through-hole or via. In addition,the top and bottom surfaces and the edges of each tab 36 defined duringthe formation of slots 38 can also be covered by the electricallyinsulative coating. The top and bottom surfaces and the edges ofdisposable part 34 defined during formation of slots 38 can also becovered with the electrically insulative coating. However, this is notrequired. Typically, however, all of the edges, surfaces and, if viasare provided, the interior surface of each via of the conductive sheetof panel 32 are covered by the electrically insulative coating.

Next, photolithographic processing techniques and metallizationtechniques known in the art and described in the above-identified UnitedStates patent application incorporated herein by reference are utilizedto define a circuit pattern 40 on one or both of the exposed surfaces ofthe electrically insulative coating deposited on the portion of theelectrically conductive sheet associated with each first PCB layer 30.

If each first PCB layer 30 is ready for use after circuit pattern 40 isformed thereon, each first PCB layer 30 can be singulated from panel 32by applying a breaking force to the tabs connecting each first PCB layer30 to disposable part 34. However, if desired, one or more additionallayers of electrically insulative coating (not shown) and circuitpatterns (not shown) can be formed over circuit pattern 40, with thevarious layers of circuit patterns interconnected in a desired mannerutilizing conventional processes. Thereafter, each first PCB layer 30can be singulated from panel 32 by applying a breaking force to each tabconnecting each first PCB layer 30 to disposable part 34.

Alternatively, each first PCB layer 30 of panel 32 can be laminated to asecond PCB layer 42 of a panel 44 shown in FIG. 4. Panel 44 includes oneor more second PCB layers 42 connected to a disposable part 46 of panel44 by tabs 48 defined during formation of slots 50 in the electricallyconductive sheet of panel 44 in the same manner described above inconnection with the formation of slots 38 in panel 32.

An electrically insulative coating is deposited on the conductive sheetforming panel 44 in a manner whereupon the top surface, the bottomsurface and the edges of electrically conductive sheet associated witheach second PCB layer 42 that were exposed during the formation of slots50 are covered thereby. If the conductive sheet is perforate, theelectrically insulative coating also covers the interior surface of eachthrough-hole or via. In addition, the top and bottom surfaces and theedges of each tab 48 defined during the formation of slots 50 can alsobe covered by the electrically insulative coating. The top and bottomsurfaces and the edges of disposable part 46 defined during formation ofslots 50 can also be covered with the electrically insulative coating.However, this is not required. Typically, however, all of the edges,surfaces and, if vias are provided, the interior surface of each via ofthe conductive sheet of panel 44 are covered by the electricallyinsulative coating.

Each second PCB layer 42 has a circuit pattern 52 formed on one or bothof the exposed surfaces of the electrically insulative coating depositedon the portion of the electrically conductive sheet associated with eachsecond PCB layer 42. If desired, each second PCB layer 42 can includeone or more additional layers of electrically insulative coating andcircuit patterns formed over circuit pattern 52, with the various layersof circuit patterns interconnected in the desired manner utilizingconventional processes.

With reference to FIG. 5, and with ongoing reference to FIGS. 3 and 4,panels 32 and 44 can be laminated together in a manner known in the art,with each first PCB layer 30 positioned in registry with a correspondingsecond PCB layer 42 to form a multi-layer PCB assembly 60. Appropriatetechniques known in the art can be utilized to form one or moreelectrical connections between each circuit pattern 40 and thecorresponding circuit pattern 52. For simplicity of description, theformation of these one or more electrical connections between circuitpattern 40 and corresponding circuit pattern 52 will not be describedherein.

As shown best in FIG. 5, tabs 36 of panel 32 do not overlay tabs 48 ofpanel 44 when panels 32 and 44 are laminated together. In this manner,the PCB layers 30 and 42 forming each multi-layer PCB assembly 60 can besingulated from their disposable parts 34 and 46, respectively,independent of each other. If desired, however, one or more tabs 36 and48 can be in alignment with each other when panels 32 and 44 arelaminated.

With reference to FIGS. 6 and 7, and with continuing reference to FIGS.3-5, each tab 36 and 48 will now be described with respect to anexemplary tab 36 of panel 32. However, it is to be appreciated that eachtab 48 of panel 44 is similar to each tab 36 of panel 32 and, therefore,the following description of exemplary tab 36 is applicable to each tab48.

As shown in FIG. 6, exemplary tab 36 extends between first PCB layer 30and disposable part 34. To facilitate breaking, exemplary tab 36includes a narrowing 62, also known as a Charpy notch, along its length.This narrowing 62 enables exemplary tab 36 to break at a well-definedposition whereupon exemplary tab 36 separates into a first part 64 thatremains attached to first PCB layer 30 and a second part 66 that remainsattached to disposable part 34.

The ends of slots 38 on opposite sides of exemplary tab 36 define arecess 68 within a perimeter 70 of first PCB layer 30. For purpose ofthe present description, perimeter 70 of first PCB layer 30 includes theouter edge 72 of first PCB layer 30 and the imaginary extension 74 ofouter edges 72 across each recess 68. As shown, the narrowing 62 of eachtab 36 is within perimeter 70 of first PCB layer 30. Hence, whenexemplary tab 36 separates into first part 64 and second part 66, adistal end 76 of each first part 64 terminates within recess 68.

With reference to FIG. 8, and with continuing reference to all previousFigs., since first PCB layer 30 and exemplary tab 36 include anelectrically conductive sheet 78, like sheet 4 in FIG. 1, coated with anelectrically insulative coating 80, like coating 8 in FIG. 1, breakingexemplary tab 36 exposes a small portion 82 of the edge of electricallyconductive sheet 78 and the surrounding electrically insulative coating80. Since only the distal end 76 of first part 64 of exemplary tab 36includes small portion 82 of electrically conductive sheet 78 exposed,substantially all of the edge of electrically conductive sheet 78 iscovered by electrically insulative coating 80 and, more particularly,the insulating edge layer of electrically insulative coating 80.Accordingly, inadvertent electrical contact with the edge ofelectrically conductive sheet 78 covered with the insulating edge layerof electrically insulative coating 80 is avoided.

The electrically conductive sheet of first PCB layer 30 and second PCBlayer 42 can be utilized to conduct heat away from electrical componentsdisposed on one or both surfaces thereof. In addition, the electricallyconductive sheets of PCB layers 30 and 42 of each multi-layer PCBassembly 60 can be utilized to provide power and ground to electricalcomponents disposed on the outward facing surfaces of multi-layer PCBassembly 60. This is accomplished by connecting the power lead of eachintegrated circuit disposed on multi-layer PCB assembly 60 to theconductive sheet of one PCB layer 30 and 42 and connecting the groundlead of each integrated circuit to the conductive sheet of the other PCBlayer 30 and 42. The conductive sheet of each PCB layer 30 and 42 canthen be connected to an appropriate one of a power terminal and a groundterminal of an external power supply via the small portion 82 of theedge of the electrically conductive sheet exposed on the first part 64of one or more tabs 36 by suitable fixture means.

With reference to FIG. 9, in accordance with a second embodiment of theinvention, a first PCB layer 90 is fabricated in the same manner asfirst PCB layer 30 discussed above in connection with FIG. 3. In thissecond embodiment, however, one or more tabs 92 extend outward from aperimeter 94 of first PCB layer 90 and connect it to a disposable part96 of a panel 98 that also includes first PCB layer 90 and tab 92. In amanner similar to PCB layers 30 and 42 and tabs 36 and 48, respectively,first PCB layer 90 and tabs 92 can be formed from an electricallyconductive sheet having its top and bottom surfaces and edges coatedwith an electrically insulative coating. However, in this secondembodiment, the electrically insulative coating can be omitted from oneor more tabs 92 or can be removed from one or more tabs 92 afterdeposit. One or more of tabs 92 can each include a mounting hole 100that can be utilized to couple tab 92 to mounting hardware or externalelectrical circuitry, such as a power supply.

A circuit pattern 101 can be formed on one or both exposed surfaces offirst PCB layer 90 utilizing photolithographic processing techniques andmetallization techniques known in the art. Once first PCB layer 90 hascircuit pattern 101 formed on one or both exposed surfaces thereof,first PCB layer 90 and each tab 92 can be singulated from panel 98,especially disposable part 96, and utilized as is. If desired, however,one or more additional layers of electrically insulative coating andcircuit patterns can be formed over circuit pattern 101, with thevarious layers of circuit patterns interconnected in a desired mannerutilizing conventional processes. Thereafter first PCB layer 90 and eachtab 92 can be singulated from panel 98.

With reference to FIGS. 10 and 11, if desired, panel 98 can be laminatedto a panel 106 in a manner known in the art with first PCB layer 90 inregistry with a second PCB layer 102 of panel 106 to form a multi-layerPCB assembly 104, shown best in FIGS. 11-13. Second PCB layer 102 ispart of panel 106 that includes tabs 108 and disposable part 110. One ormore tabs 108 can each include a mounting hole 112 that can be utilizedto couple tab 108 to appropriate mechanical hardware or electricalcircuitry. In a manner similar to PCB layers 30 and 42 and tabs 36 and48, respectively, second PCB layer 102 and tabs 108 can be formed froman electrically conductive sheet coated with an electrically insulativecoating. However, in this second embodiment, the electrically insulativecoating can be omitted from each tab 108 or can be removed from each tab108 after deposit.

A circuit pattern 114 can be formed on one or both surfaces of secondPCB layer 102 utilizing photolithographic processing techniques andmetalization techniques known in the art. Once first PCB layer 90 andsecond PCB layer 102 are laminated in registry, appropriate techniquesknown in the art can be utilized to form one or more electricalconnections between circuit pattern 101 and the circuit pattern 114.

With reference to FIG. 12, and with continuing reference to FIG. 11,next, a breaking force can be applied to each tab 92 and 108 tosingulate first and second PCB layers 90 and 102 and, hence, multi-layerPCB assembly 104, from disposable parts 96 and 110. To facilitate theapplication of a breaking force to each tab 92 and 108, tabs 92 and 108can be positioned on first and second PCB layers 90 and 102 so that theydo not overlay each other. As shown, all of each tab 92 and all of eachtab 108 remains with first and second PCB layers 90 and 102,respectively. To this end, a breaking force applied to each tab 92 andeach tab 108 causes it to break from disposable part 96 and 110,respectively. To enable each tab 92 and 108 to break cleanly fromdisposable parts 96 and 110, a break or score line can be formed at theboundary of each tab 92 and 108 and each disposable part 96 and 110 toweaken the mechanical connection therebetween. A suitable breaking forcecan be applied to each tab 92 and 108 by a mechanical press having a ramwith a suitably shaped tip for causing the breaking force to be appliedto the tab, especially the score line.

With reference to FIG. 13, and with continuing reference to FIGS. 11 and12, at a suitable time one or more electrical components 120, such as apackaged integrated circuit, an unpackaged flip-chip integrated circuit,a resistor, a capacitor and/or an inductor can be coupled to appropriatepoints of circuit pattern 101 and/or circuit pattern 114 of multi-layerPCB assembly 104 in a manner known in the art. Moreover, as shown inFIG. 14, one or more tabs 92 and/or 108 can be coupled to a mountingfixture 122 or an electrical fixture, such as a power supply 124. Sinceeach tab 92 is part of an electrically conductive sheet 130 associatedwith first PCB layer 90, and since each tab 108 is part of anelectrically conductive sheet 132 associated with second PCB layer 102,connecting one or more tabs 92 to one terminal of power supply 124 andconnecting one or more tabs 108 to the other terminal of power supply124 biases electrically conductive sheets 130 and 132 accordingly. Theprovisioning of electrical power to electrically conductive sheets 130and 132 in this manner simplifies the provisioning of electrical powerto each electrical component, e.g., electrical component 120, coupled toone or both outward facing surfaces of multi-layer PCB assembly 104.

In addition, other electrical components, such as one or more capacitors134, can be connected between adjacent pairs of tabs 92 and 108. Theinclusion of one or more capacitors 134 between adjacent pairs of tabs92 and 108 reduces the need to install filter capacitors on one or bothof the outward facing surfaces of multi-layer PCB assembly 104 toprovide electrical filtering for electrical components disposed thereon.

Like the distal end of exemplary tab 36, the distal end 136 of each tab92 and the distal end 137 of each tab 108 includes an exposed edge ofelectrically conductive sheet 130 and 132, respectively. In addition,all or part of the top surface and/or bottom surface of the electricallyconductive sheets 130 and 132 associated with adjacent pairs of tabs 92and 108, respectively, can be exposed in order to facilitate theconnection of electronic components, such as capacitors 134,therebetween.

As can be seen, the present invention provides a printed circuit boardhaving one or more printed circuit board layers each of which has aconductive plane that extends to the edge of the printed circuit boardbut which is substantially, but not completely, covered by an insulatingmaterial. The edge of the conductive layer not covered by the insulatingmaterial is positioned on the edge of a tab which is utilized to couplethe board to a disposable part of a larger panel that the printedcircuit board is formed from during fabrication. The exposed edge of theconductive layer becomes exposed upon breaking the tab and singulatingthe printed circuit board from the disposable part of the panel.

The conductive layer of each circuit board layer can serve the dualpurpose of conducting heat away from electrical components disposed onone or both surfaces of the printed circuit board or printed circuitboard layer and providing power or ground to the electrical components.

The present invention has been described with reference to the preferredembodiments. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. Forexample, multi-layer PCB assembly 60 was described as being formed bylaminating together PCB layers 30 and 42. However, a multi-layer PCBassembly can be formed from three or more PCB layers laminated togetherand electrically connected in a desired manner. Moreover, an electricalcomponent, e.g., capacitor 134, was described as being connected to tabs92 and 108 of adjacent PCB layers 90 and 102 of multi-layer PCB assembly104. However, an electrical component can be connected between tabs ofadjacent or non-adjacent PCB layers of a multi-layer PCB assembly havingthree or more PCB layers. It is intended that the invention be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

1. A circuit board comprising: a conductive sheet sandwiched between aninsulating top layer and an insulating bottom layer, the top and bottomlayers and the conductive sheet defining an edge that includes an edgeof the conductive sheet; and an insulating edge layer covering the edgeof the conductive sheet, wherein: the insulating edge layer includes atleast one opening where part of the edge of the conductive sheet isexposed; the part of the edge is within a perimeter of the circuitboard; the part of the edge is on a tab attached to the circuit board;and the tab extends into a recess in the circuit board.
 2. The circuitboard as set forth in claim 1, wherein the conductive sheet includes atleast one via therethrough.
 3. The circuit board as set forth in claim1, wherein the insulating layers are formed from a common dielectricmaterial deposited on the conductive sheet.
 4. The circuit board as setforth in claim 3, wherein the dielectric material is conformally coatedon the conductive sheet.
 5. The circuit board as set forth in claim 1,wherein at least one of the top and bottom layers has a circuit patternformed thereon.
 6. The circuit board as set forth in claim 1, whereinthe part of the edge is exposed in response to separating the circuitboard layer from a panel.
 7. The circuit board as set forth in claim 1,wherein the tab terminates within the recess.